An automatic transmission for an automobile includes a mechanism that measures the rotational speed of a rotary shaft of the automatic transmission, and measures the torque that the rotary shaft transmits, and then performs transmission control for controlling the automatic transmission itself, or output control for controlling the output of the engine. As such a device for measuring torque is a device disclosed in JPH01254826 (A) that converts the amount of elastic torsional deformation of the rotary shaft that transmits torque to a phase difference of output signals from a pair of sensors, and measures the torque based on the phase difference.
FIG. 64 illustrates a first example of a conventional torque measurement device that includes this kind of construction. This torque measurement device includes a pair of encoders 2 that are fastened on the outside of the rotary shaft 1 at two locations in the axial direction of the rotary shaft 1, and sensors 3 that correspond to each of the encoders 2 and that are supported in a housing that is not illustrated in the figure. The outer-circumferential surfaces of these encoders 2 function as detected sections, and the magnetic characteristics of these encoders 2 change in an alternating manner at a uniform pitch in the circumferential direction. The pitches at which the magnetic characteristics vary in the circumferential direction on the outer-circumferential surface of these encoders 2 are equal to each other. On the other hand, the sensors 3 are arranged so that the detecting sections of the sensors 3 face the outer-circumferential surfaces of the encoders 2. These sensors 3 cause the output signals that are outputted from the sensors 3 to change according to the change in the magnetic characteristics on the outer-circumferential surfaces of the encoders 2 that the detecting sections face.
The output signals from the sensors 3 change periodically as the encoders 2 rotate together with the rotary shaft 1. The frequency and period of this change are values that correspond to the rotational speed of the rotary shaft 1. Therefore, it is possible to find the rotational speed of the rotary shaft 1 based on that frequency and period. Moreover, as the rotary shaft 1 transmits torque, the rotary shaft 1 undergoes elastic torsional deformation, which causes relative displacement between the encoders 2. As a result, the phase difference ratio (=phase difference/1 period) between the output signals from the sensors 3 changes. This phase difference ratio is a value that corresponds to the amount of elastic torsional deformation of the rotary shaft 1 due to transmitting torque. Therefore, the torque that the rotary shaft 1 transmits can be found based on this phase difference ratio.
When trying to apply the torque measurement device of this first example of conventional construction to an automatic transmission for an automobile, the torsional rigidity of the rotary shaft 1 that is the target of torque measurement is high, so there is a problem in that it is difficult to sufficiently maintain the amount of elastic torsional deformation of the rotary shaft 1, and the resolution of the torque measurement becomes low. Moreover, it is necessary to install the two sensors 3 so as to be separated in the axial direction, so there is also a problem in that it becomes difficult to arrange two harnesses 4 that run from these sensors 3. Furthermore, in order to support the sensors 3 in a highly precise relative positional relationship, it is necessary to provide supporting and fastening sections in the housing, and thus there is also a problem in that processing of the housing becomes complicated.
In regard to this, JPH01254826 (A) discloses a torque measurement device in which the sensors have a unit-like construction. FIG. 65 illustrates a second example of a conventional torque measurement device that has this kind of construction. In this torque measurement device, the detected sections of a pair of encoders 2a that are fastened at two locations in the axial direction of the rotary shaft 1 extend toward the center section in the axial direction, and detecting sections of a pair of sensors of a single sensor unit 5 that is placed in the center section in the axial direction of the rotary shaft 1 faces the detected sections of the encoders 2a. However, in this case of applying the torque measurement device of this second example of conventional construction to an automatic transmission for an automobile as well, even though the installation of the sensor unit 5 is simplified, it does not mean that the problem of low resolution of the torque measurement has been solved.
Moreover, JPH02017311 (U) discloses a torque measurement device having construction that uses a torsion bar. More specifically, the torque measurement device of this third example of conventional construction is constructed so that encoders are fastened to the outer-circumferential surfaces of a pair of rotary shafts that are arranged along the same line, and these rotary shafts are connected by a torsion bar that undergoes elastic torsional deformation more easily than these rotary shafts. In this case, the amount of relative displacement in the rotational direction between the encoders can be made large due to the elastic torsional deformation of the torsion bar that occurs when transmitting torque, so it is possible to improve the resolution of the torque measurement. However, even when the torque measurement device of this third example of conventional construction is applied to a counter shaft of an automatic transmission for an automobile, it is difficult to sufficiently improve the resolution of the torque measurement. In other words, an input gear and output gear are fastened at two locations in the axial direction of the counter shaft, and the portion of this counter shaft that undergoes elastic torsional deformation during the transmission of torque is only the portion that is between these gears. The space in the axial direction of this portion is small, and it is difficult to sufficiently lengthen the dimension in the axial direction of the torsion bar that is to be placed in this portion, so it is not possible to sufficiently maintain the amount of elastic torsional deformation of the torsion bar.
As other related literature that is related to the present invention is JP2010185478 (A). A torsion bar having high fatigue strength and that is able to handle large stress loads, and a manufacturing method for manufacturing that torsion bar are disclosed in JP2010185478 (A).
[Related Literature]
[Patent Literature]
[Patent Literature 1] JPH01254826 (A)
[Patent Literature 2] JPH02017311 (U)
[Patent Literature 3] JP2010185478 (A)